European Patent No. 139,066 relates to a foil embossing unit comprising a fixed frame supporting a pair of embossing rollers cooperating with each other and mounted for rotation on respective pairs of bearings. One of the rollers is a drive roller and therefore connected to a motor, while the other is driven by the drive roller and therefore free to rotate about a respective axis. The drive-roller bearings are fixed with respect to the frame, whereas the driven-roller bearings are movable with respect to the frame, substantially independently of each other and in opposition to elastic means, in a direction perpendicular to the traveling direction of the foil between the two rollers.
The above device has several drawbacks, due to automatic in-service adjustment of the two roller axis positions being limited to only one direction, which means the two rollers must be positioned extremely accurately, and therefore at great cost, when setting up the unit, and the set position of the rollers checked periodically. Moreover, in the event, as frequently happens, of the rollers shifting slightly from the set positions, the above limitation results in increased vibration, uneven wear of the rollers, and possibly also embossing defects.
One solution to the above drawbacks is proposed in European Patent Application No. 686,782, which relates to an embossing unit similar to the one described in European Patent No. 139,066, except that the driven-roller bearings are movable with respect to the frame, substantially independently of each other and in opposition to elastic means, in a first direction and a second direction respectively perpendicular and parallel to the traveling direction of the foil between the two rollers.
European Patent Application No. 686,782 enables automatic in-service adjustment of the two roller axis positions in two perpendicular directions, but only at the expense of a mechanically complex and therefore high-cost device, which, by failing to also provide for automatic adjustment along the roller axes, only partially solves the aforementioned drawbacks.